The present invention relates to a variable displacement swash plate type compressor capable of controlling displacement by controlling the inclination angle of the swash plate based on the pressure in a crank chamber.
A variable displacement swash plate type compressor includes a swash plate, which is accommodated in a crank chamber. The inclination angle of the swash plate is variable. High-pressure control gas is supplied to the crank chamber, and the pressure in the crank chamber is controlled by controlling the amount of the supplied control gas. Accordingly, the compressor displacement is controlled. Specifically, when the crank chamber pressure is raised, the inclination angle of swash plate is reduced, which reduces the stroke of the pistons in the cylinder bores. Accordingly, the displacement is reduced. In contrast, when the crank chamber pressure is lowered, the inclination angle of the swash plate is increased, which increases the stroke of the pistons in the cylinder bores. Accordingly, the displacement is increased.
However, high-pressure refrigerant gas, which has been compressed in compression chambers, may be introduced as blow-by gas into the crank chamber through between each piston and the corresponding cylinder bore (through side clearances). When such blow-by gas enters the crank chamber, the crank chamber pressure cannot be set to a control target value, and the inclination angle of the swash plate deviates from a desired angle. Desired displacement thus cannot be achieved.
In a case in which a variable displacement swash plate type compressor is installed in a refrigerant circuit (external refrigerant circuit) of a vehicle air conditioner, it is preferable that the amount of lubricant circulated in the refrigerant circuit be limited to improve the cooling efficiency. However, if the amount of lubricant circulated in the refrigerant circuit is reduced, lubrication between the pistons and the cylinder bores deteriorates, which will increase wear of the cylinder bores. As a result, the amount of blow-by gas entering the crank chamber is increased.
For example, Japanese Laid-Open Patent Publication No. 2003-206856 discloses a technology for reducing wear of cylinder bores. As shown in FIG. 6, a piston 90 disclosed in the document has a tapered surface 92 at the distal end of the outer circumferential surface of a columnar portion 91. The piston 90 also has a chamfered portion 93, which is continuous with the tapered surface 92. The diameter of the outer circumferential surface of the columnar portion 91 decreases toward the distal end. When coating is applied to the outer circumferential surface of the piston 90, the above described configuration prevents the coating material from remaining at the distal portion of the columnar portion 91, so that no annular protrusion is formed at the distal portion. As a result, the cylinder bore is prevented from being scratched by such an annular protrusion. Wear of the cylinder bore is thus reduced. Further, the structure of the tapered surface 92, the chamfered portion 93, and the decreasing diameter toward the distal end of the piston 90 allows lubricant to enter between the piston 90 and the cylinder bore.
However, according to the document, the shape of the piston 90 changes from the distal end toward the proximal end, particularly sharply at a section from the chamfered portion 93 to the tapered surface 92. As a result, the side clearance, which is formed between the piston 90 and the cylinder bore, sharply narrows. This makes it difficult for lubricant to enter between the piston 90 and the cylinder bore. Accordingly, the lubrication between the piston 90 and the cylinder bore deteriorates, and wear of the cylinder bore increases. As a result, the entering amount of blow-by gas will be increased.